These probes have built-in transmitters and are powered by low voltage supplies. They are intended for environmental monitoring.
The 525 has a Standard Probe type sensor and will operate with a supply voltage as low as 5.5 V. Its output signal is 0-2.5 V and it has a very low power consumption. It is ideal for use where solar panels are used as power source. The 525 T is a combined DO and temperature probe with two output signals.
The Model 505 can be fitted with Profile or Ocean sensors, and is intended for incorporation into sondes where the millivolt output from the sensor cannot be used directly.